There is an epidemic of obesity in the United States which is accompanied by the populace's effort to lose weight. Low-carbohydrate diets are a popular alternative to traditional dietary approaches to weight loss. These diets may result in short-term weight loss and the improvement in disease risk normally seen with weight loss, but their effects on long-term weight loss and disease risk are unknown. We propose a randomized, controlled trial to systematically assess health claims about low-carbohydrate diets, and explore concerns expressed about these diets by health professionals. We will compare the short- and long-term effects of the Atkins diet (low-carbohydrate) and the Dietary Approaches to Stop Hypertension (DASH) diet (high-carbohydrate) on weight loss, body composition, physiological markers of energy and weight regulation, markers of cardiovascular disease (CVD), bone health, and renal function. The study blends applied behavioral research with basic mechanistic research to clarify the interaction between the behavior and biology of weight and energy regulation. We will recruit and enroll overweight and obese adults who wish to lose weight, and who agree to be randomized to either the DASH or the Atkins diet for the duration of the study. The randomized population will include 240 participants, 60percent of whom will be women and 20percent of whom will be ethnic and racial minorities so that our outcomes can be generalized to the US population. In Phase I, study subjects will participate in an intensive 6-month behavioral intervention program designed to facilitate weight loss. This will be followed by a maintenance phase (Phase II) in which counselors provide support to participants to maintain weight loss for 2 years. The primary outcome is a change in weight between the beginning of the study and the end of 30 months of follow-up. [unreadable] [unreadable]